Entomology and Other Sciences 291 



II. Artificial Controls 



c. Farm practices 



d. Mechanical devices 



e. Insecticides. 



I. As a rule natural controls are not at all or are not readily 

 utilizable artificially, although a knowledge of these control factors will 

 enable one to assist the factors which are optimum for minimizing insect 

 troubles. 



(a) Climatic control includes all climatic factors having a definite 

 relation to the absence or abundance of this or that insect. These fac- 

 tors include winter conditions, humidity, soil moisture, precipitation, 

 wind and seasonal weather. 



(b) Natural enemies are important factors in minimizing insect 

 abundance and not infrequently of suddenly checking insect outbi'eaks. 

 However, aside from the control by parasites or predators in nature, 

 little has been accomplished. The introduction of parasites of exotic 

 insects accidentally brought into this country is simply an atempt to 

 renew the balance as it occurs in the native home of the insect pest 

 and is a very profitable and desirable activity. Many examples are 

 available. The cottony cushion scale, introduced into California, threat- 

 ened to wipe out the citrus industry in that state but the inti-oduction 

 of certain lady-bird beetles from Australia checked it and apparently 

 has ever since held the scale pest in thorough control. The parasites 

 and predatory enemies of the browntail and gypsy moths are playing 

 a significant part in holding these pests in check and minimizing spread. 

 The digger wasp parasite introduced into Hawaii has completely sub- 

 dued certain foreign grub worms which a few years ago threatened 

 to make cane-growing unprofitable. This list of examples could be in- 

 creased many times. Only recently has much attention been directed 

 toward artificially utilizing these natural enemies. 



Under natural enemies are included not only the insects which are 

 parasitic or predaceous on harmful insects but also the many birds and 

 mammals which prey upon insects. We would also include insect dis- 

 eases which are endemic and epidemic. 



II. Artificial controls may be conveniently grouped into three divi- 

 sions, control by (c) farm practices, (d) mechanical devices and (e) 

 insecticides. At the present time we immediately think of insecticides 

 as the most important of the insect controls. However, too little atten- 

 tion has been given the important subject of farm practices. In the 

 orchard, greenhouse or vegetable garden it is possible to utilize more or 

 less costly insecticide treatments but such is not usually true in the 

 case of general farm crops such as corn, wheat and clover which are 

 grown less intensively and where the cost of spraying might absorb all 

 profits. Here, then, we must usually adopt certain so-called farm prac- 

 tices. Even in the orchard, the vegetable garden and elsewhere, the 

 farm practices — orchard and garden practices — are becoming more and 

 more recognized as factors deserving of more attention. 



(c) Control by farm practices refers to the practices which are 

 or may be a part of the ordinary farm operations such as cultivation. 



